The present invention relates generally to afterburners for aircraft gas turbine engines, and in particular to a readily replaceable heat shield for an afterburner fuel injection tube.
Afterburning or reheating is one method of augmenting the basic thrust of a turbine engine. An afterburner increases thrust by adding thermal energy to a stream of turbine exhaust gas and engine bypass air located aft of the core engine. The afterburner includes several fuel injection tubes, known as spray bars, for dispersing fuel into the stream of gas. Each tube extends radially inward from an outer wall into the engine exhaust and has multiple spray orifices for dispensing fuel. The afterburner also includes flame stabilization devices, known as flameholders, for creating regions of reduced gas velocity to facilitate effective combustion. The afterburner is typically located in close proximity to a mixing duct, or mixer, that combines a portion of the stream of bypass air with the turbine exhaust gas to improve performance. The mixing duct is a cylindrical shell with a plurality of circumferentially-spaced passages, known as chutes, for delivering bypass air into the stream of turbine exhaust gas.
Each of the fuel injection tubes of the afterburner is protected by a heat shield, a housing which encloses the tube and has an internal channel for delivering cooling air along the tube. A plurality of openings are spaced along the heat shield for alignment with the spray orifices to permit fuel to be injected from the tube into the gas stream.
Heat shields are periodically replaced due to burning damage, thermal cyclic fatigue, or coking residue. Ideally a heat shield should be replaceable in a short time so that aircraft down-time is minimized. Unfortunately, some types of heat shields require many hours to repair because they are not readily replaceable. For instance, an entire augmentor assembly must first be removed from an engine before obtaining sufficient access to remove some heat shields. On other designs, the heat shield is permanently attached to a support structure, such as by welding. Replacement of these heat shields requires substantial time and expense.
In general, a heat shield of the present invention protects a fuel injection tube of a turbine engine afterburner. The afterburner has a generally cylindrical outer wall and a duct member spaced inwardly from the outer wall defining a boundary between a core duct for flow of turbine exhaust gas and a bypass duct for flow of cooling air. The fuel injection tube extends from the outer wall inwardly through an opening in the duct member to the core duct. A first portion of the fuel injection tube is in the bypass duct and a second portion of the fuel injection tube is in the core duct. The heat shield comprises a base for supporting the heat shield in the core duct, the base being adapted for attachment to the duct member. The base has a front side with a first mounting surface, a first fastener hole extending through the base, and a recess in the base. A housing encloses the second portion of the fuel injection tube. The housing has an internal channel therein open at an end thereof for receiving the fuel injection tube, a second mounting surface, a second fastener hole, and a tab protruding from the housing. The tab is sized and shaped for being received by the recess in the base. The housing may be releasably secured to the base at a mounting position on the base wherein the tab is received by the recess, the mounting surfaces are engaged, and the second fastener hole is positioned in aligned registration with the first fastener hole so that a fastener may be inserted to secure the housing to the base.
In another aspect, a combination of the present invention includes a mixer chute and an attachable heat shield for an afterburner of a gas turbine engine. The afterburner has a generally cylindrical outer wall, a duct member spaced inwardly from the outer wall defining a boundary between a core duct for flow of turbine exhaust gas and a cooling duct for flow of cooling air, and a fuel injection tube extending from the outer wall inwardly to the core duct. A first portion of the tube is in the cooling duct and a second portion of the tube is in the core duct. The mixer chute comprises a passageway extending from the duct member into the core duct for delivering cooling air from the cooling duct into the flow of turbine exhaust gas. The heat shield comprises a housing releasably attachable to the chute at a mounted position. The housing has an internal channel for receiving and enclosing the fuel injection tube, and at least one fastener hole in the housing for receiving a fastener to releasably attach the housing to the chute at the mounted position.
Other features of the present invention will be in part apparent and in part pointed out hereinafter.